BOSTON (Reuters) - A former State Street Corp executive on Wednesday became the second person to plead guilty to participating in what U.S. prosecutors say was a scheme to defraud six clients through secret commissions on billions of dollars of trades.

Richard Boomgaardt, who lives in Britain and was head of State Street's transition management desk for Europe, the Middle East and Africa, pleaded guilty in federal court in Boston to conspiring to commit wire fraud and securities fraud.

Boomgaardt, a citizen of Canada and the Netherlands, entered his plea two weeks after Edward Pennings, a former senior managing director in State Street's London office, pleaded guilty to a conspiracy charge in connection with the same scheme.

The two men are among three former State Street executives to face U.S. charges in connection with the probe. The Boston-based bank in January agreed to pay $64.6 million to resolve related U.S. criminal and civil investigations.

Boomgaardt, 44, in court acknowledged having engaged in conduct outlined in a five-page statement of facts. He faces up to five years in prison when he is sentenced. U.S. District Judge Denise Casper scheduled his sentencing for Dec. 13.

The case followed a 2014 settlement between State Street and the UK Financial Conduct Authority in which the bank paid a fine of 22.9 million pounds, or $38 million at the time, for charging the six clients markups on certain transactions.

From 2010 to 2011, Boomgaardt, Pennings and Ross McLellan - a former executive vice president at the bank - conspired to add the secret commissions to fixed-income and equity trades executed for certain clients, prosecutors said.

The clients were using a State Street unit that helps institutional customers move investments between asset managers or liquidate large investment portfolios, prosecutors said.

McLellan has pleaded not guilty to securities fraud and wire fraud charges. His trial, originally scheduled for Oct. 23, was delayed by a federal judge on Friday to June 4 to allow McLellan's lawyer to gather evidence overseas.

The cases in U.S. District Court, District of Massachusetts, are U.S. v. McLellan, et al, No. 16-cr-10094, and U.S. v. Boomgaardt, No. 17-cr-10167.